Method for thermal polymerization of hydrocarbons



J. w. 'rHRocKMoR'rcN 2,328,864

Sept.y 7, '1943.

METHOD Fon THERMAL roLYMERIzATIoN oF HYDRocARoNs Filed June 21. 1939 df .Rr

DI #E INVENTOR Jahn W 77zr'oclrmarla7zv P BY 57W /VM ATTORNEY Patented Sept. 7, "jj

terrine" rufe This invention rentes to" imefovemerite m-te 'rmolytic 'conversion of: hydrocarbon fluids and U become the practice to recirculate certain low I "molecular weight hydrocarbons, the boilingponts ofwhion are below` the usualY motoryfuel boiling `1"a`nge, to the: Tconversion zone in: order to inif `Itle l thermal treatment; `practIce-n1"the" operatonfoffthrmalfbblsfmezae' 'on plan'ts to separate from the recycle' gases,

reaction or 4were A'largely unaffected; by 11th-e condi-l `favorable to successfolyfolymerlaation olv hierherv "moreemar' weight hydrocarbons;oartieolarlytne `sses'." It hasfrtller been established that operiemore@artiouanyloonoemed with improvements lin thermal polymerization of l'lydrocarbon'gases l `v z toihydrocarbonsbollmg wthinxmotor melboilingr` rocesses which dependlupon thermalffxneana f aloref-efo ,effecting conversion reactionegit' has" tions ifttemperature, pressure and? reaction. time Caand C4 hydrocarbons,`whicl hydrocaronsgenez erally comprise the principal constituents "ofthe, largng stock of thermal rpolyrnerzationvproce nateCihf/drocarbons and lightergaseefromthe j `chargegandefrom the gases recycled to -a couver sonprocesar Whether 'or no ttlleA conversion oe dronten;

1 Company, fChioag'o, 111.-,` a, oortemperature is the only criterionlor `determn- `lng what gases shall be recycled to the-conversion;

Zone may 'be a matter of opniongbut inany event l the general commercial practice in `the art of converting low molecular Weight hydrocarbons to by drocarbons :boiling 4Within the motor fuel-bolle ing range shows that it is the' accepted practice 4to.` remove 1pz hydrocarbons as Well asrmetlrane;

andhydrogen from the hydrocarbons recycledto` hydrogen, methane"emoA 'ce hydrocarbon; Sincere was` believed:` that these eases interfered Wlthl the i; elem e cracking and polymerization very `-mltnetrle A `pan'ficulargnyclrocafrbons ndergoinetreatment.

For` example, ethane feqmres a meenemen@ fc-rickin'g temperatrexto -formhnsaturatewcorn' pounds whlchwill polyrnerizethando the higher bomng'hydrooerbonsag propane and lontane/. f f general, `the greater the number ofl'carbozr atome" in 1 the compound; Vthe :less drastic j is the" treat@ mntrequred to `decompc'se tilpartl'cularlyziwth' thee` View `of forming unsaturated "nyrooareone.

` Tlsh'as been particularly clearly shown by the' ves'tgator's' who'4 have Workdjwtn 'pure Al'n'zfd' carbone such as ethanef, propane and bota-rie; f tughas likewise beenl 'Shown `that,` :if mixture l of 510Wl molecular Weight paranic `llyclrfocarborls f is processed at atemperature that produce'ssubi YQ stantial conversion of thewmember of loc/"fast molecular weight, the yield `ofrnotor fuejltboilng,

range hydrocarbons produced-Tromtle molecularweight hydrocarbonss greatly dimmer `ehed due tocoke formation and/foil formatonb poijmers'ofehigherthan motorjfuel fbollinfgrange@` N Thasvthe prior artteaches thatit snanadva taggn the Wnversicn of hydrocarbnieastoelim included inthe Vgases recycled to theLconverson zone ci a'thernjlalpo'lynlerzaton process designed ftoconvert low `boiling hydrocarbons to hydroarbons ofnmotor `fuelbflinemange and if essentially complete Y:reoore1'yfoffthe rG 3- hydrocarbons from the converslonprodncts isprac-tced and these Cef hydrocarbons fare included as a 1cornsttnent` :ol thegass rwled:aellrprsieglylehyeld ,Ofghy-,v`

drooarbdnsbeiline within-motorie@boilinerange: results;`V vThe improvementin yield is; especially noticeable "when chargng hydrocarbon gasesthat, a'rlowfor substantallyiree o f unsaturates: `Bylorry-in.Y unsaturates f1: mear a" gas `which fuel hydrocarbons obtanablefrom the ptherrrralv conversion ci low boiling; hydIOCalbOIlS-j "It is afurther object of kthisfnventiol'l" t tnao\ l vde a method ffor .increasing the yield olqmetor fuel e hydrocarbons obtainable frorng; the 'thermal tallynrcreasing operatingcosts- V e Other objects iand advantages will `become apof a chamber.

nection with polymerization of hydrocarbon gas consisting chiefly of saturated C3 and C4 fractions, it is to be understood that the invention is applicable to the treatment `of hydrocarbon gases in which either paraninic or olennic hydrocarbons preponderate.

Referring to the drawing, the numeral l indicates a line lcontrolled by valve 2 through which gas is charged to the system. This gas may be gas from refinery operations such as oil cracking, or from natural gas, or a mixture thereof,

and consists predominantly of Ca and C. hydrocarbon fractions.k The gas may be Lcharged under Apressure of approximately 200 to 500 pounds per square inch. The gas passes from line l and cooler 4 from which it passes to feed tank 5. In feed tank 5 the gases may be in substantially liquid condition or in a condition of mixed gas and liquid, depending uponthe ccmpositionof Although the invention will be described inrconing the vreaction coil through line 22 are immediately and quickly chilled in exchanger il to-a vvalve 2 and is cooled by passage through the I the gas and the conditions `of temperature and pressure maintained. Usually the temperature will be from 70 to 120 F.and thepressure from 200 to 500pounds per square inch. y The liquefied gas'is withdrawn fromV the feed'tank 5 through line v'l by means' of pump 9 in which the gas is raised to the desired pressure'for charging to the conversion zone. This pressure Vmay be from approximately 200 to 2500 or more pounds? per square inch. The compressed gas which is substantially in the'liquid state is charged throughy 'heat exchanger Il wherein iti passes in indirect heat exchange with hot products fromthe reaction A coil which will be subsequently described and may be preheated Ato a temperature-of 600" tor 900 F. The preheated gasleaves thefexchanger throughy line [Band passes'intothe inlet of heating r coil |75 located-in furnacefll. `Inthe heating-licei] the gases are" heated while main-A tained under' the aforesaid pressure, to temperal tures'ranging from approximately 95,0"Vfto`1250"y F.,'dep`ending upon the pressure, the composition 'of the charge and upon the nature of the product-desired. `A temperature'vrange-of 1025?` to 1125'F. has been foundto be particularly' 'effecf tiveon a charge of hydrocarbon'gas composed principally ofpropaneand butarie'.- If hi'ghpressures are employed, the temperature will not be substantially ineexcess olf"1100 If low prese sures of theforder of 350 pounds persquare inch are employed,'the temperature willpreferably be From the heating coil i5 the'h'e'atedgases pass to reaction coil I9 wherein the products arefmainair in order to control the temperature'in the reaction coil. It isznecessary toprovide forboth heating and cooling nfl-'the'reactioncoilsince the net heatkof reactionfof the hydrocarbons may be either endothermic orfexothermic, depending upon theunsaturate'content `of the gases charged to the system. The reaction products upon leavtemperature below that at which conversion takes place, by indirect heat exchange relation with gases charged to the system- The temperaturel is preferably lowered to below the temperature at which polymerization occurs, for example 700 l. or lower, but in no case should the temperaturel be below that at which satisfactory :frac-V K tionation of the products may be obtained. The chilled products may be further cooled as conditions require by passage through heat exchanger 23, the products then passing through line 25V controlled by Valve 27 into the lower portion of primary fractionator` 29. At valve 27 the pressure may be reduced if necessary so that the pressure in the primary fractionator will be maintained between approximately 325 to 450 pounds per square inch. rPhe pressure and temperature of theproducts entering fractionator 29 are so regulated that C4 and lighterY material can be separated as an overhead. product and sothat the overheadproducts can be handled without compression. Vapforization and fractionation of' the products takes place in .tower 29. Nothing heavier than C4 hydrocarbons is taken off over-.

head. s The bottoms will contain all material boil-` ingy above C4 hydrocarbons as well as some C4 and lighter hydrocarbons. yA portion ofthe bottoms from fractionator 29 may be returnednto' the'fractionator as reflux Aby means of line 3|,

valve 32, pump 34, cooler 36, and line 38,1 the principal portion being passed through line r.3|

into approximatelythe midegsection of secondary fractionator 39. Thisffractionator may be main-L tained at a pressure v"of 1'75fto' 275 4pounds per A square inch and 'functions principally as a debutanizer, `.the overhead comprising predomi-v nantly Csand C4 hydrocarbons. .Additionalheat for proper fractionation may be supplied-from outside sources by meansV of reboiler 40. The

liquid; now. substantially free.` from C4 hydrocarn j bons and lighter gases, is withdrawn from the f bottom of reboiler 40 through line 4I and heater 42 and -passed through line. 43 todistillate fractionator 44. The debutanized liquid is heatedin v heater. 42 to -a suf'cient temperatureto remove 4 Y substantially all motorr fuel boiling range hydroy carbons overhead from 'distillate fractionator 44.'A

Open steamr-` may be .fed into 'fractionator 44 through line 45 and valve 46 to facilitate the dis-` tillation.'l Distillate fractionator .44 may be oper`V f ated at a pressure of 20 to 100 pounds per square inch.v Additionalheat for proper fractionation may be'supplied by means of reboiler 41. The

bottoms stripped of gasoline boiling fractions are removed from reboiler 41 through line 48 and withdrawnfrom the system. Motor fuel boiling .range hydrocarbon vapors rare taken from distillate fractionator 44 through line 49, completely condensed to liquid in cooler 5I, and collected as a liquid product in accumulator 53. Endpoint ydistillate motor fuel is removed from the system A' through line 55. A portion of the .end point dis-l tillate may be returned to distillate fractionator 44 as reflux by means of pump 51, valve:59'and line (il.`

VReturning to secondary fractionator 39, th

vapor overhead comprising principallyvCa and C4 hydrocarbonsis removed through line63, condensed in cooler and collected in accumulator f El. Any uncondensedvmaterial may vbef-vented from the system through line G9 and valveifl. 'Iheliqueed condensate comprising principally Csand vC4 hydrocarbons-may be withdrawn lfrom accumulator 61 by means offline 12, pump 1.3, valve '141,line 15, and line 11 `and returnedas a recycle 'stock to fresh feed line I wherein itis mixedfwiththe fresh feed charged tothe system. A portion ofthe condensate withdrawn from accumulator' 67| maybe returned to secondary fractionator 39 as reflux by means of line 18 and valve19.` f f 'f The overhead vaporsfrom primary fractionator 25)` comprising C4` and `lowerhydrocarbons together with hydrogen is `withdrawn from the fractionator through line '80, partially condensed in cooler 8| and collected in separator 83 wherel in the liquid and vapors are separated under such conditions of temperature and pressure thatthe maior portion of C and C4 hydrocarbons is 'condensed.- The liquid condensate is: withdrawn from -separator 83 by means `of pump 05, line '81, va1ve`88, and cooler 9|, withdrawn from thecooler throughline 02, passed into line 15A wherein it is mixed with condensate withdrawn from accumulator 61,l and returned through line L`1'| to fresh feed line I and lfiereinfurther mixed with fresh gas charged to the system. A portion of the liquid condensate recovered in separator 83 may bereturned as reflux to primary fractionator 29 by means of line |l3and'valve 95. Unconden'sed gases are withdrawn from 'separator 83 through line 91, valve SSL-and line |I, cooled incoole |03 and fedto the lower portion of high pressure absorb-er '|05 stripper through line |21, condensed in cooler |29 and collected in accumulator |3I. The pressure at which the absorber oil stripper is oper- |33 and line |35;.1Condensate recovered in ac,-

cumulator |3| isre'rnoved through line |31, pump |39, valve |4|, line |42 and` valve |43 and'passed into line'15 wherein it is mixed with condensate recovered from the p rimaryfractionatcr 29 and secondary fractionator 39 and returned to fresh feed line wherein a further mixture with fresh gases charged tothe system occurs. A portion of the condensate withdrawn from accumulator |3| may be supplied as reflux to` the top of flash -tower ||8 byv closing` or partially closing valve .|43 in 1ine|42 and passing it through line |44 controlled by valve |44' and line |50. A portion of the condensatewithdrawn from accumulator |3| may also be returned to stripper |23 as re` flux through line |45 and valve |40. `Alternawherein the gases may be contacted with,vv and a portion thereof absorbed in, gas oil or other suitable liquid absorptive medium. v The pressure at which `the high pressure absorber *operates may gases fed to theabsorber, theuobiect being to line |01 and removed'fromthe system. Rich oil bottoms are withdrawn from the bottom of the absorber through line |09eand pump passed through heat Vexchanger and heater ||3 `and I|5 respectively, wherein the temperature ofthe rich oil is raised to desired flash tower-conditions, and i then through line ||1 into fiashtow'er wherein the rich oil is stripped of dissolved lowboiling hydrocarbons, principally `Cz` fractions.` "Flash towei` IIB maybe operated .atatpressure of approximately 350 to 450 poundsQabottom temperature of 300 to 400 F. and' a top temperature of 100 to 200 F., the conditions maintainedr bef ing such' as to substantially completely strip the richoil of any C2 hydrocarbons. The pressure maintained in iiash tower `||8 isalways sum-f l ciently high so that C2 fractions'in the overhead vapors maybe `charged backk to `the feed'` tank through line ||9 without compression and7`will there, toa large extent, liquefylwhon Vrnix`ed`with theheavier portionof the charge.` f The partially stripped absorption medium `is removed from the flash` tower throughline |2| and passed'to the mid-section of absorberA oil stripper |23 man` tained at lower pressure thanflash tower-WIS, and any remaining normally gaseous' hydrocarbons such as Ca and Cifractions removed overhead.` Additional `heat to `facilitate the frac; tionation may be supplied by reboiler |25. Low

i be approximately 300to 500 pounds and the temperature about 60 to 120 F. The pressure and `temperature conditions lrnaintainedin this absorber as well `asthe ratio of gas oil circulated depend somewhat uponthecomposition ofthe tively, reflux may be supplied to the flash tower by withdrawing liquid feed from tank 5 by means of line 1, pump 9, line |5|, control valve |52, and line|50.

Lean absorption oil from `which the lowmclecular weight hydrocarbons have been completely s trippedin stripper |23 is removed from reboiler |25 through line |53 by means of pump |54,

passed through lline |55, 'exchanger H3, wherein l the temperatureis reduced by indirect heat eX- change with bottoms fromthe absorber, passed through line |53,v further cooledin cooler l'land returnedfthrough line to the top of high pressure absorber |05. l l l While I have set forth one means bywhich my wherein it is mixed with overhead vapors from secondaryfractionator` 39 and passed to cooler 65 `and accumulator 61. are charged to the system bythe means just den scribed, valve 2 is closed. Inthis method ofoperation condensate removed from accumulator 61 containing the fresh material charged to the system, is removed through line l2, pump 'I3 and line |55, valve Ili'l being opened and valve 'Id closed. `The mixture then passes through line 93 into the top of primary fractionator 29; IValve S5 may be open or closed or in an 'intermediate position, depending upon the amount of reflux required. Usually, however, valve S5 will be closed in this method of operation.` VIt is apparent that the fresh feed` may be split anda portion of the feed charged to the system by each of themeans described. i l i i It will be seen, therefore, that C2 fractions as wellas Csi. and C4 fractions' are` separated., from the reactiongases and returned to the feed tank.

for recycling' throughthe vconversion zone` together with fresh feed gases charged to the system, all without the use ofv any gas compression steps;

The advantages of my process will` be more clearly apparent from the specific* examples of boiling hydrocarbon fractionsvaporized inthe stripper may be-removed from\ the top of 'the When the fresh feed gases` several commercial scale operations, the critical data of which are set forth below:

TABLE I y Run 1 Run 2 Analysis of net fresh feed' C3. .mol per cent..-. 61. 3 72. 4

C4.- -.d- 38.7 27. 6 Unsaturates per cent.. 30-35 30-35 Reaction coil outlet temperature .F.. 1,082 1, 085 Reaction coil outlet pressure -.lb./sq. in.. 475-500 475-500 Reaction time seconds.. 38. 1 37. 1 Yield end point poly gasoline per 1,000 cu. it. of

` net fresh gas changed gallons-. 8.6 9.8

Recycle ratio A 2. 9 3.0 Analysis of recycle C,-.. mol per cent.- 2. 3 2. 3 C2 l-- do-.-. 2.9 2.4 Cz.-. ---do-.-. 10. 2 13. 7

yC3. .-.do-.-. 61.0 69.4 C4- .d0..-- 23.6 10.6 05.'. 0.... 1.6

1 Unsaturated. Y

' TABLE II Run 3 Run 4 Run 5 Outlet temp. heat. coil ..F. 1, 114 1, 137 1, 130

Outlet temp. react. coil.. .....F.. 1,060 l, 085 1,078

Pressure react. coil .lbs. ga.. 475-500 475-500 475-500 Net fresh feed:

Gai/hr.-. 1, 19o 1, 570 1, 24o 682 897 710 30-35 30-35 30-35 71 73 76 29 27 24 4,560 7, 42o 7, 42o Bbls./day 2, 605 4, 240 4, 240

CH., .mol per cent.- .4 1.8 1. 5 d 4. 5 2. 4 2. 9 5.8 13. 7 14. 5 23.0 23.1 22. 6 47. 0 44. 0 44. 3 19. 3 15. 0 14. 2

Recycle ratio vol. basis 3 82 4. 72 6.00 Per cent Cg-conversion per pass.... 27 23 16 Yields Run 3 Run 4 Run 5 Weigh: Weight Weigh: per cef/lt BbL/day per cent BOL/day per cent BbL/day Gas 45 41. 0 40 Gasoline. 39 188 l 49. 5 309 54. 5 280 vFuel oil.--" 16 59 9.5 42 5. 5 19.5

1 Part of the yield increase is, of course, due to the overall higher recycle ratio reducing the degree of overpolymerization as expressed in ratio of fuel oil to gasoline yield. However, the major part of the additional recycle material constitutes just the extra amount of ethane, as is indicated by the conversion per pass oi propane.

Inspection of gasoline Gravity API.. 53. 5

Vap. Pr. #Reid Octane number..- IBP leavingV the unit in the residue gas. the polymerization process is not charged for purposes of calculation with C3 and heavier fractions which may escape asy residue gas through In this' way incomplete or improper separation from lighter gases which are withdrawnfrom the system. In all of the runs indicated, the same heating and reaction coils were used. Reaction time is computed as the period in seconds during which the charge is subjected to the average temperature of the reaction coil which, for the examples cited, lies Within the range of 1060 F. to 1085 F. The reaction time was substantially the same for all of the runs in Tables I and II.

A comparison of Runs 1 and 2, Table I, indicates the effect on yield of increasing the proportion of C2 and C3 fractions recycled to the conversion zone with the fresh feed. Although the conditions of temperature, pressure, recycle ratio and composition of fresh feed are substantially the same in both cases, the yield of motor fuel end point polymer gasoline is increased by 1.2 gallonsy per 1000 cubic feet of net fresh gas charged in Run 2. This is due to the increased amount of C2 and C3 fractions in the recycle charged to the conversion Zone. There is some difference in amount lof C3 and C4 fractions in the composition of the net fresh feed, Run 1 having 38.7 mol of C4 while Run 2 shows but 27.6 mol C4 fraction. Ifthis difference in C4 content Were the only difference between Runs 1 and 2, it would be expected thatthe yield of polymer gasoline from Run 1 would be the highest since it is well known in the art that under the operating conditions indicated, the yield of polymer gasoline is higher from C4 fractions than from C3 fractions, the proportion of unsaturates being Substantially the same in each case. It is thus apparent that in contrast to what might well be expected, increasing the proportion of Cz and C3 fractions returned to the conversion zone, in-

creases the yield of polymer gasoline.

In Table II, results of Runs 3, 4 and 5 are shown wherein under like operating conditions the effect of increasing still further the proportion of C2 fraction recycled to the conversion zone is clearly Ibrought out. This increase of C2 fractions is accomplished yby obtaining additional C2 fractions from the residue gas thereby increasing the l proportion of C2 in the recycle and by increasing the recycle ratio which brings about a further increase in the proportion of C2 fraction charged to the conversion Zone with the fresh feed. As the amount of C2 recycled is increased, the yield of polymer gasoline is increased. Run 3 having 10.3 mol of Cz fraction in the feed to the heating coil produced 39% by weight of polymer gasoline. When the C2 fraction in the heating coilfeed was increased to 17.4 mol as in Run 5, the yield in weight of polymer gasoline increased to 54.5, a figure entirely unexpected in view of the teaching of the art since C2 fractions do not polymerize to 'gasoline boiling range hydrocarbons to` an appreciable degree under the operating conditions shown herein. The yield is even more unusual when the composition of the net fresh gas charged to the system is considered, Run 5 having 24 mol C'4s and Run 3 only 29 mol'% C4s.

The increased yield is not due entirely to the increased C2 recycle but is also due to high recovery and recirculation of C3 fractions andto adjustment of conversion conditions whereby high recycle ratios may be obtained.

Although specific methodsof converting substantially saturated lowmolecular weight hydrocarbons have been' shown and described, it is to be understoodk that the invention is not limited to the specific form shown and described but is he following claimsnl m yI claim:

ratedhydrocarbons. consisting of substantially 1113A andgCql hydrocarbons to"hydrocarbonsl boiling V i Uwithin a range suitable for liquid motor fuel i comprising subjecting said gases in a reaction y k l 1. Process for convertingY predominatelysatul,

:zone to pressures `oi. 400.1902500 pounds per squareL` i finch'and temperaturesof 1000" to`1250 F., maintaining such lgases'in a heated and compressed miistate fora sufcient period oftirne to convert 'a' *substantial portion of `said gases Ito liquid motor fuel hydrocarbons, t said conditions of' pressure,4

x `temperatureand time being such that C2 Vhydrof Cgafraction containingthe major portion of the C4, C: and Ci` hydrocarbons. the `Cz hydromixture chargedltothe reactionzone being belowv that` which will. cause rise e in temperature during lreaction..` 15" carbons` do nnot polyxnerize 'to ,any appreciable e degreaffractionating the converted productsinto liquids consisting chiefly off hydrocarbons above i carbpns including a major portion but not all of` the ethane and ethylene, and a fraction contain`y ing the major portion of the hydrogen and methane, eliminating the last mentioned fraction from l the system, recycling `andeniixwinggthe second e mentioned fraction With thesaid predominately saturatedhydrocarbons consisting of substan-` tially C3 and C4 hydrocarbons Aat such a rate as to maintain a recycle ratio of approximately 2.9 to 6, the? unsaturated content of the resulting `2. Process in accordance with `claim`1 in whichsuiiicient gas containing ethane and ethylene is e f, recycled. so` that the mixed gas chargedto the reactionV Zone, contains i approximately 17.4 mol percent ofI Ciu hydrocarbons.

f "JoHN W. THROCKMORTON. 

